Several magnet systems to provide guidance for magnetic medical devices for navigation within a patient have been devised or are under development. An example of such a system is disclosed in commonly assigned app. Ser. No. 09/189,633, "Articulated Magnetic Guidance System," which is hereby incorporated by reference in its entirety. A device disclosed therein includes a bed, a bed articulation system, a pair of x-ray sources, a coil or magnet articulation system, and an optional pair of additional magnets. The magnet articulation system comprises an articulation support, servo control mechanisms to provide movement of a coil or a permanent magnet along an arcuate arm both through a polar angle and in a radial direction. Optionally, the entire arm may also be pivoted through an azimuthal angle. The arm itself may comprise a track and gimbal assembly. Additional embodiments described in the referenced application include one in which the arm itself is moveable via an articulation support, another in which the magnet or coil is mounted on a pivotable ring support, and another in which the magnet or coil is mounted as an effector on a robotic arm. In the latter embodiment, it is desirable for the effector and all other parts of the robotic arm to be provided with exclusion zones to prevent accidental contact with a patient, with medical personnel, and, of course, with other items that might be damaged by such contact.
Other magnetic systems that provide guidance for magnetic medical devices within a patient are disclosed in commonly assigned app. Ser. No. 09/211,723, filed Dec. 14, 1998, "Open Field System for Magnetic Surgery," which is also incorporated by reference in its entirety. A plurality of magnets are configured and arranged to provide a magnetic field effective within an operating region of a patient to navigate a magnetic medical device within the operating region while providing access to the patient for imaging and other purposes. A single magnet is arranged and configured to provide a magnetic field along at least one of a plurality of oblique axes extending through the operating region. One or more magnets are arranged and configured to provide a magnetic field along each of the other of the oblique axes. The magnetic fields generated by the magnets are effective to controllably navigate the magnetic medical device within substantially the entirety of the operating region. A preferred embodiment of the system described in this reference comprises three magnets in three mutually perpendicular planes, arranged so that their axes at least converge and more preferably intersect in the operating region. The magnets are arranged in an open configuration, so that the patient typically does not have to extend through a magnet coil to reach the operating region. In a preferred embodiment, the magnets comprise coils that are fixed with respect to one another in a generally downwardly facing hemispherical shell.
Still other magnetic systems providing guidance for magnetic medical devices navigated within a patient are disclosed in commonly assigned Provisional app. Ser. No. 60/095,710, filed Dec. 14, 1998, "Method and Apparatus for Magnetically Controlling Catheters for body Lumens and Cavities," which is also incorporated by reference in its entirety. The apparatus of the invention disclosed therein generally comprises a magnet system for applying a magnetic field to a magnet-tipped distal end of a medical device. The magnetic field provides a field that can navigate, orient, and hold the distal end of the medical device in the body. The apparatus also includes a computer for controlling the magnet system. Imaging devices connected to the computer provide images of the body part through which the catheter is being navigated. Displays are provided of these images. A controller connected to the computer has a joystick and a trigger to enable a user to input points on the displays for two-point and three-point navigation. The magnet system itself is preferably a set of electromagnetic coils that can be disposed around the body part to create a magnetic field of variable direction and intensity. Magnet systems suitable for such use are disclosed in U.S. Pat. No. 4,869,247, issued Sep. 26, 1989, "Video Tumor Fighting System," and U.S. Pat. No. 5,125,888, issued on Jun. 30, 1992, entitled "Magnetic Stereotactic System for Treatment Delivery," the disclosures of both of which are also incorporated by reference in their entirety.
In the commonly assigned application entitled "Device and Method for Specifying Magnetic Field for Surgical Applications," app. Ser. No. 09/020,798, filed Feb. 9, 1998, and which is hereby incorporated by reference in its entirety, six normally conducting or superconducting coils are arranged in a rectangular box or helmet. With the Z-axis defined in the direction of the axial component of the head, the X- and Y-coil axes are rotated 45.degree. from the sagittal plane of the head. Biplanar fluoroscopy cameras linked to a real-time host system are provided. Both cameras are calibrated to the six-coil host helmet design, in which three pairs of opposing coils on mutually perpendicular axes are provided. X-ray generators are also provided for the cameras.
In yet another commonly-assigned application entitled "Method and Apparatus Using Shaped Field of Repositionable Magnet to Guide Implant," app. Ser. No. 09/020,934, filed Feb. 2, 1998, and which is herein incorporated by reference in its entirety, an apparatus comprising a moveable magnet assembly having a plurality of fiducial marks is disclosed. In an exemplary embodiment, the magnet assembly may be a gantry supporting either a strong permanent magnet or a superconducting electromagnet, although a strong permanent magnet may require additional articulation to compensate for its lack of current control and magnitude. The magnet assembly may be automatically controlled to provide the needed orientation, location and coil current required to align its magnetic field with the desired motion of a magnetic object to be guided. Localizers and camera-like sensors are provided to detect the fiducial marks on the magnet assembly, and additional fiducial markers may be placed on the patient's body. Medical imaging devices are used to display the location of the magnet relative to the volume of interest in the patient and the location of the implant. Various means are provided for moving the magnet.
Each of these devices and methods provides some success in being able to provide magnetic field orientations in all directions in sufficient strength for the intended applications. Nevertheless, even with specially designed systems, it is still difficult to completely avoid interference with the imaging system while achieving full functionality of the magnetic guidance system. In many of the above systems, this difficulty becomes apparent in the requirement to provide limitations in the movements of one or more large magnets or their supporting structures, or in limitations imposed on movements and positioning of an imaging system relative to the magnet system. In addition, the systems designed to date, including many of the above, have been quite large and expensive, or are restricted in purpose and application.
The magnets used in magnetic navigation are typically superconducting electromagnets which provide controllable, strong magnetic fields. One drawback of superconducting electromagnets is the cryogen system required to keep the coil at the approximately 4.degree. K needed to safely maintain the superconducting state of the coil. The size and weight of the cryogen system makes it difficult to support and move the superconducting electromagnetic coil and also restricts the orientations in which the coil can be positioned. While substantial progress has been made in the design of cryogenic systems, there are limits on the position and orientation of the dewar for the cryogen, which limits the orientations in which the associated coil may be placed. The size of the cryogen system also restricts where the coil can be positioned relative to the patient.
It would therefore be desirable to provide a relatively inexpensive system for magnetically assisted surgery that could produce a magnetic field in any orientation and at sufficient strength for use in medical applications. It would also be desirable if the system could provide field lines through a given procedure point in space (i.e., the location of the magnetic medical device) that could be easily and safely changed with a minimum of articulation of the magnet, so that the effect of the various exclusion zones in an operating region could be minimized. It is also desirable to provide such a magnet system where the magnet is compact and capable of being moved in any orientation relative to the patient to maximize the freedom of navigation within the patient.